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We have a UM2 unit which is behaving a bit strange for quite some time now, in regards to the side cooling fans.

I'd like to know whether others have experienced the same type of issues and how to best troubleshoot them.

Also, I'd like to know how the UM2 material properties fan setting affect the fan speed.

When I slice an object with Ultimaker 2 machine profile aka "UltiGCode", it seems that the gcode is generated so that the fans are on full speed (M106 S255) on the layer that is on height 0.5mm.

As a standard in Cura, the first layer, layer 0, is set to 0.3mm (to ensure good first layer adhesion). Therefore, if I slice an object with a layer height of 0.2mm then the fan will be full on from the second layer (layer 1) since 0.3+0.2=0.5mm.

If I slice it for a layer height of 0.1mm, then Cura will generate an M106 S127 for the second layer (layer 1) to set a fan speed of 50%. Then the third layer will be at 0.5mm and thus generate a M106 S255.

When having 0.05mm layer height, fans will likewise be in 25%, 50%, 75% and finally 100% in the same manner.

Now, my questions:

1. What does the "Fan speed" of a UM2 Material profile do? I can change this between 0 and 100%.

If the gcode is like I described earlier, different M106 Snnn codes, what will the fan speed do?

Is it relative to the last M106 Snnn gcode executed? Or does it work in some other way?

2. The side fans are sometimes intermittent so that the come on and off. I find it very strange. Here is a video (dropbox link to H264-encoded video, about 8 MB) of layer 1 (the second layer) which should then be at 50%.

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I suspect that there's a loose wire somewhere that's making the fans stop intermittently... Also, what is that awful screeching noise when the head is moving?

The default 'full on at' setting in Cura is 0.5mm, but I'm wondering if that's the best choice... Originally Daid had phased in the fans to reduce the cooling of the head due to ground effects when the fans were right by the bed, I thought... In practice, these settings are going to have the fans on full within just 2 or 3 layers for most prints anyway... is that really the intent, or should the 'full on at' height be greater?

Another to be aware of, although I don't think it's the case here - is that when lit only by the built-in LEDs - and especially at low brightness levels - the fans can sometimes appear to spin slowly, or backwards, due to strobing of the PWM'd LEDs, even when the fans are at full speed - very weird to see.

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The default 'full on at' setting in Cura is 0.5mm, but I'm wondering if that's the best choice... Originally Daid had phased in the fans to reduce the cooling of the head due to ground effects when the fans were right by the bed, I thought... In practice, these settings are going to have the fans on full within just 2 or 3 layers for most prints anyway... is that really the intent, or should the 'full on at' height be greater?

IIRC, the default height for the fan to be full on is 5,0mm, under the expert settings, I'm only 99% sure since I have been playing around with a lot of settings for the past couple of weeks so I may have changed this without me realising, but I'm almost certain the fanspeed scales linear to 100% at 5,0mm.

1. What does the "Fan speed" of a UM2 Material profile do? I can change this between 0 and 100%.

If the gcode is like I described earlier, different M106 Snnn codes, what will the fan speed do?

Is it relative to the last M106 Snnn gcode executed? Or does it work in some other way?

I think it's along those lines. I haven't looked at the g-code that much, but what I found during prinitng was this:

My settings have the fan start at 0 on layer 1 to 100% at height 5,0mm (usually this is layer 50 because I tend to print at 0,1mm).

So after say 3mm of printing if I go into the 'Tune' menu, under fan speed it would say 60% and I can then change that up or down to my liking for that layer, but at the start of the next layer my manual input will be overridden (because that's in the g-code).

Only after reaching those 5,0mm (and the fan being permanently on full) will any manual adjustments be permanent (nolonger overridden at the start of the next layer).

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I suspect that there's a loose wire somewhere that's making the fans stop intermittently..

Yes. This. Slide the black netting up above the head and look at the fan connectors - they are red and black cables going down into the head. Is one of them almost disconnected? Tug gently on all the wires to see if one is loose.

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Thanks for all comments. This is a pre-prod unit which have had some teething issues but it's been working well overall.

It's most likely a damaged JST connector because we can make the fan stop/start by nudging it. Now if I only could find the correct crimping pliers and JST connector...aaargh. I deeply dislike JST connectors. Too hard to disconnect without wear to cables. I guess they are not designed to be decoupled too often.

The schreeching sound is most likely a rubber band misaligned, it's on the gigantic todo list

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The screeching could also be the x axis cross-rod scraping on the side panel - the tolerances are quite tight, I've discovered this week, or one of the motors - most likely the y-motor scraping on the side wall because the pulley has shifted out a bit.

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It was was the cables from two(!) fan JST connectors (male side) that had bit by bit starting to come loose/been ripped from the JST connectors. I did not have the proper size JST connectors to crimp new ones but I made new ones by some jumper housing pins and soldered them nicely with heat shrink. Seems to work splendidly. I wonder whether the entire cable bunch need to be secured better for maintenance to survive that and millions of movements...

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